The present invention relates to a refractory material, including sprayable material, gunnable material, and trowelable material, to be used principally for coating the surface of the back-up lining of a continuous casting tundish, steel ladle, and the like.
Conventionally, refractory material capable of being applied as a coating by spraying, gunning, or troweling, has been used for repairing the surface of a continuous casting tundish, steel ladle, and the like. Refractory materials using an aggregate of magnesia are generally used in such a coating refractory, but refractory materials using an aggregate of calcia such as lime and dolomite are known as well.
When a basic refractory containing a calcia aggregate is used in a tundish, CaO in the aggregate selectively adsorbs, or as it is termed in the art, "catches", alumina and other non-metallic impurities which are contained in molten steel and which have a detrimental effect on final steel quality. The relative ability of a calcia-containing refractory to remove alumina and other impurities is referred to as the "catch capability" of the refractory. Reduction in the amount of these impurities also significantly reduces the occurrence of clogging in the tundish nozzle caused by the deposition of impurities on the inner surface wall of the nozzle. This selective catching property of CaO is metallurgically beneficial in that it results in higher purity steel.
However, when refractory material using a calcia aggregate is applied to the inner surface of tundishes and steel ladles, by any of the methods of spraying, gunning, or troweling, all of which require the use of water, cracks may be generated and material flaking or spalling may occur due to CaO in the aggregate reacting with the water (i.e. slaking) during subsequent curing, drying or preheating. Accordingly, the application of calcia-aggregate containing refractory material is currently limited to use in non-aqueous systems.
The objective of the present invention is to provide a refractory material, which can be applied by any of the methods of spraying, gunning or troweling, to a tundish or steel ladle, in either a hot or cold state, and even in a situation where water is used. This is achieved in the present invention by including in the refractory a specific synthetic dolomite aggregate having an excellent slaking resistance.